A low-cost camera which has become popular in recent years is commonly referred to as a "disposable camera" or a "film with a lens" since it contains little more than a plastic housing, a plastic lens, film and a shutter mechanism. This type of camera is designed generally for taking snapshots, and will be referred to herein as a "low-end" camera. Some commercially available low-end cameras have a built in flash unit, or stroboscope, to enable the taking of pictures in low light conditions, such as indoors. However, low-end cameras are not usually provided with means for detecting the ambient brightness and determining whether operation of the flash unit is needed. As a result, operation of the built in stroboscope provided in low-end cameras is performed manually. In the typical low-end camera provided with a stroboscope, charging of the stroboscope is commenced by the pushing of a stroboscope charging switch disposed on the camera body separately from the shutter release button.
In the above-described low-end camera, the decision as to whether or not the stroboscope will be operated depends entirely upon the photographer's judgment. An inexperienced photographer may thus take an underexposed photograph by failing to operate the stroboscope in low light conditions or may overexpose the film and waste power by unnecessarily operating the stroboscope when ambient brightness is high.
To satisfy the requirements of low cost and small space and weight, the low-end camera is required to reliably perform the aforesaid functions with a low voltage, low capacity power supply, such as a single low capacity dry cell (typically a 1.5V battery).
Cameras which are more expensive than the typical low-end camera described above are often equipped with an internal photometric circuit for judging ambient brightness and determining whether operation of a stroboscope is necessary. The typical brightness judging circuit is constructed using the combination of an internal microcomputer provided in the camera for performing various functions and an analog/digital converter or a comparator for detecting brightness. However, the power supply for a microcomputer must generally be at least as high as about 3V, and that for a comparator must be at least as high as about 2V, even if it is fabricated using low power bipolar processing techniques. Moreover, a microcomputer and comparator are expensive components and are not suitable for use in a low-end camera. These components are also high in current consumption so that a dry cell or a low capacity power supply will be rapidly consumed. This makes it difficult for a power supply consisting of a single low voltage dry cell of low capacity to drive such components as the cell may be temporarily lowered to about 1V by a load even when sufficient voltage remains in the battery to operate other circuits.
Moreover, in order to compensate for fluctuations in device characteristics due to temperature and supply voltage variations, brightness judging circuitry generally uses compensation data stored in external memory such as EEPROM (Electric Erasable Programmable Read Only Memory) or an additional temperature compensation circuit. Thus, the construction of brightness judging circuitry is even more expensive and larger than noted above. As a result, conventional photometric circuitry of the type commonly used in more expensive cameras is not well suited for use in low-end cameras.
In order to solve the foregoing problems, the assignee of the present application has proposed, in its co-pending Japanese Patent Application No. 9-357204, a low cost, low power photometric circuit and a stroboscope driving circuit which are particularly well-suited for use in a low-end camera by fabricating the major components of the photometric circuit in one integrated circuit and by adding a peripheral circuit.
However, when the aforementioned circuit uses as a light detector an inexpensive Cadmium Sulfide cell ("CdS") having poor response characteristics so as to maintain low cost, it is necessary to reduce the frequency of an oscillator used in the circuit and to enlarge a capacitor connected to the oscillator. This makes it difficult to mount the capacitor along with the remainder of the photometric circuit in a single integrated circuit chip and requires that a capacitor having a large capacitance value be mounted externally to the circuit. It is also necessary to connect an externally mounted variable resistor. The use of these external components increases the size and cost of the photometric circuit, and the camera, and hence, these external components are not preferable in a small-sized, low-end camera.